In the manufacturing of parts in a powder compacting press, the parts within a particular lot must be periodically checked in an attempt to maintain the desired green density distribution. This is done by sintering to final density and observing the final shape of the part. If the parts are unsatisfactory with respect to green density distribution as indicated by incorrect dimensions of the sintered parts, adjustments must be made on the press to adjust the pressure which is applied to the powder.
This checking and adjusting method is time consuming and costly and is subject to error. As a result, there is a high rejection rate of parts.
Therefore, an improvement by which the green density distribution of parts can be controlled without the above disadvantages would be highly desirable and an advancement in the art.
U.S. Pat. No. 4,100,598 to Stiel et al relates to compressive force detection. This patent relates to shallow die fill parts on a rotary press. The average green density is controlled.
U.S. Pat. No. 4,413,967 to Burry relates to measurement of peak force on a punch and this varies with the weight of the material. This measurement does not take into account the changes in force that come about because of changes in the die fill.
By following Stiel and Burry, one cannot make a precision sintered part of sufficient accuracy.
U.S. Pat. No. 3,910,737 to Shimada et al teaches use of an external weight apparatus for correcting weight in a powder compacting press. However, Shimada does not teach precise control of the density distribution, nor does it relate to use of two or more load cells.
U.S. Pat. No. 4,030,868 to Williams discloses a piezoelectric force transducer positioned in a powder compacting wherein the measured forces are correlated to the tablets' weight to control the punch positioning means. Williams teaches use of only one punch.
Japanese Patent 57-206,597 relates to measuring forces on upper and lower punches, but there is no teaching of computing the ratios of the forces to control density distribution.
The above references do not take into account all of the forces, even the peak forces on the part which are necessary to accurately predict and control the green density distribution in a sintered part.